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| 129 | .\" ======================================================================== |
| 130 | .\" |
| 131 | .IX Title "BitFieldTie 3" |
| 132 | .TH BitFieldTie 3 "2003-01-23" "perl v5.8.0" "User Contributed Perl Documentation" |
| 133 | .SH "NAME" |
| 134 | BitFieldTie \- Tie interface for bitfield operations |
| 135 | .SH "SYNOPSIS" |
| 136 | .IX Header "SYNOPSIS" |
| 137 | .Vb 1 |
| 138 | \& use BitFieldTie; # or use TRELoad 'BitFieldTie'; |
| 139 | .Ve |
| 140 | .PP |
| 141 | .Vb 1 |
| 142 | \& tie %num, 'BitFieldTie'; |
| 143 | .Ve |
| 144 | .PP |
| 145 | .Vb 2 |
| 146 | \& $num{'31:0'} = hex('0x1234'); |
| 147 | \& $num{'63:32'} = hex('0xabcd'); |
| 148 | .Ve |
| 149 | .PP |
| 150 | .Vb 2 |
| 151 | \& print "low byte is $num{'7:0'}\en"; |
| 152 | \& print "MSB is $num{63}\en"; |
| 153 | .Ve |
| 154 | .PP |
| 155 | .Vb 2 |
| 156 | \& my $obj = tied %num; # get object |
| 157 | \& print "Num is $obj\en"; # object prints as hex num |
| 158 | .Ve |
| 159 | .SH "ABSTRACT" |
| 160 | .IX Header "ABSTRACT" |
| 161 | .Vb 3 |
| 162 | \& This is a thin wrapper for Bit::Vector that presents a tie interface for |
| 163 | \& bit vectors. The bit vector itself can be of arbitrary size, but the |
| 164 | \& chunk size (the size of an individual bit field) is limited to 32 bits. |
| 165 | .Ve |
| 166 | .SH "DESCRIPTION" |
| 167 | .IX Header "DESCRIPTION" |
| 168 | This module allows users to access bit fields with a hash interface. |
| 169 | .Sh "Introduction" |
| 170 | .IX Subsection "Introduction" |
| 171 | This module provides two components. The first is a class, |
| 172 | BitFieldTie, that allows users to manipulate bit vectors of arbitrary |
| 173 | size using object methods. The second is a tie interface. When a |
| 174 | hash is tied to a BitFieldTie object, a hash interface can be used to |
| 175 | set or exampine bit ranges in the vector. |
| 176 | .Sh "Hash Interface" |
| 177 | .IX Subsection "Hash Interface" |
| 178 | This subsection describes using the tied hash interface. |
| 179 | .PP |
| 180 | \fISetting up a bitfield\fR |
| 181 | .IX Subsection "Setting up a bitfield" |
| 182 | .PP |
| 183 | When you tie a hash to this module, the hash becomes a representation |
| 184 | of bitfields of a number. By default, a 64\-bit integer is created and |
| 185 | initialized to zero. You can provide optional arguments to the tie |
| 186 | command to set a different size and initial value, as in: |
| 187 | .PP |
| 188 | .Vb 1 |
| 189 | \& tie %num, 'BitFieldTie', 32, '0x1234abcd'; |
| 190 | .Ve |
| 191 | .PP |
| 192 | The first optional agument is the size in bits, and the second is the |
| 193 | initial value \s-1IN\s0 \s-1HEX\s0. |
| 194 | .PP |
| 195 | \fIUsing a bitfield\fR |
| 196 | .IX Subsection "Using a bitfield" |
| 197 | .PP |
| 198 | You can then access fields of the hash. Hash keys can either be a |
| 199 | single number for single-bit access, or a range in the form of |
| 200 | <high>:<low>. The values in the hash are integers, so |
| 201 | for istance aftre the above initialization, the value of \f(CW$num\fR{'3:0'} |
| 202 | would be 13 (decimal for 0xd). The hash provides both read and write |
| 203 | access. \fBThe major restriction is that the size of the bit range |
| 204 | (i.e., high\-low+1) cannot exceed 32\-bits.\fR To access larger ranges, |
| 205 | you need to break it up into separate accesses. The main reason for |
| 206 | that restriction is that if the module allowed larger chunks, it could |
| 207 | not use integers to represent bit fields and performance would suffer |
| 208 | considerably. |
| 209 | .PP |
| 210 | \fIPrinting the bitfield\fR |
| 211 | .IX Subsection "Printing the bitfield" |
| 212 | .PP |
| 213 | Unfortunately, the tied-hash mechanism does not lend itself to object |
| 214 | methods to do un-hash-like things like pretty\-printing. You must |
| 215 | therefore use the object interface, and there is a little bit of |
| 216 | syntax involved. |
| 217 | .PP |
| 218 | .Vb 1 |
| 219 | \& $obj = tied %num; |
| 220 | .Ve |
| 221 | .PP |
| 222 | This sets \f(CW$obj\fR to the underlying object for the tied hash. The object |
| 223 | does know how to print itself (among other things). |
| 224 | .PP |
| 225 | .Vb 1 |
| 226 | \& print "Num is $obj\en"; |
| 227 | .Ve |
| 228 | .PP |
| 229 | The above statement will print \f(CW%num\fR as a hexidecimal number. |
| 230 | .PP |
| 231 | You can also interpolate the hash directly with a little bit of funny |
| 232 | syntax: |
| 233 | .PP |
| 234 | .Vb 1 |
| 235 | \& print "Num is @{[tied %num]}\en"; |
| 236 | .Ve |
| 237 | .PP |
| 238 | This is just a clever perl hack to do the same thing without explictly |
| 239 | referencing \f(CW$obj\fR. |
| 240 | .Sh "Object interface" |
| 241 | .IX Subsection "Object interface" |
| 242 | Objects of type BitFieldTie can be created in 3 ways. The first is if |
| 243 | a hash is tied to a BitFieldTie object, but no object is specified (as |
| 244 | is the case in the previous examples), one will be created. This |
| 245 | object can then be referenced by using the 'tied' operator on the |
| 246 | hash, as shown in the previous section. |
| 247 | .PP |
| 248 | Objects can also be created with the \fInew()\fR or \fIclone()\fR methods, as |
| 249 | described in the section on Object Methods. |
| 250 | .PP |
| 251 | Once an object is created, it can be easily manipulated as shown in |
| 252 | the next section. |
| 253 | .PP |
| 254 | \fIMath with Bitfields\fR |
| 255 | .IX Subsection "Math with Bitfields" |
| 256 | .PP |
| 257 | BitFieldTie ties a hash object to an object. This allows you to use |
| 258 | convenient hash syntax to access bit fields. To do math, however, you |
| 259 | need to manipulate the object directly. The perl builtin-function |
| 260 | tied will give you the object associated with a tied hash. |
| 261 | .PP |
| 262 | .Vb 2 |
| 263 | \& my %v1; |
| 264 | \& tie %v1, 'BitFieldTie', 64, '0x0000ffff0000cccc'; |
| 265 | .Ve |
| 266 | .PP |
| 267 | .Vb 1 |
| 268 | \& my $v1 = tied %v1; |
| 269 | .Ve |
| 270 | .PP |
| 271 | The above code creates a new 64\-bit number tied to the hash \f(CW%v1\fR. The |
| 272 | underlying object is assigned to \f(CW$v1\fR. Say we had a similar definition |
| 273 | for v2: |
| 274 | .PP |
| 275 | .Vb 3 |
| 276 | \& my %v2; |
| 277 | \& tie %v2, 'BitFieldTie', 64, '0xffff333300003333'; |
| 278 | \& my $v2 = tied %v2; |
| 279 | .Ve |
| 280 | .PP |
| 281 | You can still access bitfields using hash syntax on \f(CW%v1\fR and \f(CW%v2\fR. You |
| 282 | can now also call object methods on \f(CW$v1\fR and \f(CW$v2\fR. For instance: |
| 283 | .PP |
| 284 | .Vb 2 |
| 285 | \& $v2->bitwise_and($v1); |
| 286 | \& print "$v2"; |
| 287 | .Ve |
| 288 | .PP |
| 289 | The above prints: \*(L"0000333300000000\*(R". Keep in mind that as mentioned |
| 290 | above, when you convert an underlying BitFieldTie object to a string |
| 291 | (as in the print statement), the string is a hexadecimal |
| 292 | representation of the number. |
| 293 | .PP |
| 294 | \fIObject methods\fR |
| 295 | .IX Subsection "Object methods" |
| 296 | .PP |
| 297 | The following are the object methods that BitFieldTie objects respond to. |
| 298 | .ie n .IP "new($size, $hexstring) \s-1OR\s0 new($obj)" 4 |
| 299 | .el .IP "new($size, \f(CW$hexstring\fR) \s-1OR\s0 new($obj)" 4 |
| 300 | .IX Item "new($size, $hexstring) OR new($obj)" |
| 301 | Class method that creates a new object and returns it. Arguments are |
| 302 | optional, if a \f(CW$size\fR and/or \f(CW$hexstring\fR is specified, it works just as |
| 303 | the argument list to tie. If an object is provided, that object is |
| 304 | cloned, and the clone is returned. |
| 305 | .Sp |
| 306 | \&\fInew()\fR can also be called as an object method. So the following two |
| 307 | statements are identical (assuming \f(CW$obj\fR is a BitFieldTie): |
| 308 | .Sp |
| 309 | .Vb 2 |
| 310 | \& $new = $obj->new(); |
| 311 | \& $new = BitFieldTie->new($obj); |
| 312 | .Ve |
| 313 | .ie n .IP "new_dec($size, $decimal)" 4 |
| 314 | .el .IP "new_dec($size, \f(CW$decimal\fR)" 4 |
| 315 | .IX Item "new_dec($size, $decimal)" |
| 316 | Same as new, except that the second argument is treated as a decimal |
| 317 | argument, instead of a hex string. |
| 318 | .IP "\fIclone()\fR" 4 |
| 319 | .IX Item "clone()" |
| 320 | Returns a new BitFieldTie object that is identical to the old one |
| 321 | \&\s-1EXCEPT\s0 that it is not tied to any hash. |
| 322 | .IP "\fIstringify()\fR" 4 |
| 323 | .IX Item "stringify()" |
| 324 | Returns hexadecimal object as a string. This is called automatically |
| 325 | when you include a BitFieldTie object in double\-quotes. |
| 326 | .ie n .IP "extract($hi, $low)" 4 |
| 327 | .el .IP "extract($hi, \f(CW$low\fR)" 4 |
| 328 | .IX Item "extract($hi, $low)" |
| 329 | Returns the specified bit range from the object as an integer. Since |
| 330 | the return value is an integer, the size (i.e., \f(CW$hi\fR \- \f(CW$low\fR + 1) must |
| 331 | be <= 32. |
| 332 | .ie n .IP "store($hi, $low\fR, \f(CW$value)" 4 |
| 333 | .el .IP "store($hi, \f(CW$low\fR, \f(CW$value\fR)" 4 |
| 334 | .IX Item "store($hi, $low, $value)" |
| 335 | Stores the \f(CW$value\fR (an integer!) in the specified bit range in the |
| 336 | object. Since the return value is an integer, the size (i.e., \f(CW$hi\fR \- |
| 337 | \&\f(CW$low\fR + 1) must be <= 32. Also, the \f(CW$value\fR must be an integer, not a string. |
| 338 | .IP "\fIclear()\fR" 4 |
| 339 | .IX Item "clear()" |
| 340 | Sets all bits in the bit vector to 0. |
| 341 | .IP "\fIsize()\fR, size($numbits)" 4 |
| 342 | .IX Item "size(), size($numbits)" |
| 343 | Sets/Gets the size (in bits) of the number, depending on whether or |
| 344 | not an argument is given. |
| 345 | .IP "left_shift($numbits)" 4 |
| 346 | .IX Item "left_shift($numbits)" |
| 347 | Left shifts the number. |
| 348 | .IP "right_shift($numbits)" 4 |
| 349 | .IX Item "right_shift($numbits)" |
| 350 | Right shifts the number. |
| 351 | .IP "bitwise_and($obj)" 4 |
| 352 | .IX Item "bitwise_and($obj)" |
| 353 | Does a bitwise and between the calling object and \f(CW$obj\fR. Stores the |
| 354 | result in the calling object. For example: |
| 355 | .Sp |
| 356 | .Vb 1 |
| 357 | \& $v1->bitwise_and($v2); |
| 358 | .Ve |
| 359 | .Sp |
| 360 | has the C equivalent of: |
| 361 | .Sp |
| 362 | .Vb 1 |
| 363 | \& v1 &= v2; |
| 364 | .Ve |
| 365 | .IP "bitwise_or($obj)" 4 |
| 366 | .IX Item "bitwise_or($obj)" |
| 367 | Same as bitwise_and, except it performs an \s-1OR\s0 function. |
| 368 | .IP "bitwise_xor($obj)" 4 |
| 369 | .IX Item "bitwise_xor($obj)" |
| 370 | Same as bitwise_and and bitwise_or, except it performs an \s-1XOR\s0 function. |
| 371 | .IP "\fIbitwise_not()\fR" 4 |
| 372 | .IX Item "bitwise_not()" |
| 373 | Flips every bit in the number. |
| 374 | .ie n .IP "divide($obj, $remainder)" 4 |
| 375 | .el .IP "divide($obj, \f(CW$remainder\fR)" 4 |
| 376 | .IX Item "divide($obj, $remainder)" |
| 377 | Divides the calling object by \f(CW$obj\fR and stores the result in the |
| 378 | calling object (i.e., /=). \f(CW$remainder\fR is initialized to the |
| 379 | remainder. \f(CW$obj\fR can be an integer, in which case an object the same |
| 380 | size as the calling object is created for it. |
| 381 | .IP "multiply($obj)" 4 |
| 382 | .IX Item "multiply($obj)" |
| 383 | Multiplies the calling object by \f(CW$obj\fR and stores the result in the |
| 384 | calling object (i.e., *=). \f(CW$obj\fR can be an integer, in which |
| 385 | case an object the same size as the calling object is created for it. |
| 386 | .IP "add($obj)" 4 |
| 387 | .IX Item "add($obj)" |
| 388 | Adds \f(CW$obj\fR to the calling object. \f(CW$obj\fR can be an integer, in which |
| 389 | case an object the same size as the calling object is created for it. |
| 390 | .IP "subtract($obj)" 4 |
| 391 | .IX Item "subtract($obj)" |
| 392 | Subtracts \f(CW$obj\fR from the calling object. \f(CW$obj\fR can be an integer, in which |
| 393 | case an object the same size as the calling object is created for it. |
| 394 | .IP "compare($obj)" 4 |
| 395 | .IX Item "compare($obj)" |
| 396 | Does a comparison on the calling object and \f(CW$obj\fR (which may be an |
| 397 | integer). Returns \-1 if the calling object is smaller, 0 if they are |
| 398 | equal, and 1 if the calling object is greater that \f(CW$obj\fR. Both the |
| 399 | calling object and \f(CW$obj\fR are treated as \s-1SIGNED\s0 integers for the |
| 400 | purposes of comparison. |
| 401 | .IP "ucompare($obj)" 4 |
| 402 | .IX Item "ucompare($obj)" |
| 403 | Same as compare, but the calling object and \f(CW$obj\fR are treated as |
| 404 | \&\s-1UNSIGNED\s0 integers. |
| 405 | .Sh "Tying an Existing Object to a Hash" |
| 406 | .IX Subsection "Tying an Existing Object to a Hash" |
| 407 | If you create a BitFieldTie object with \fInew()\fR or \fIclone()\fR, it begins |
| 408 | life not tied to any hash. You can manipulate it with object methods, |
| 409 | but if you want to access bit fields with hash syntax, you will need |
| 410 | to tie it to a hash first. Here is an example |
| 411 | .PP |
| 412 | .Vb 2 |
| 413 | \& my $obj = BitFieldTie->new(64, '0xdeadbeefcafe0123'); |
| 414 | \& tie %h, 'BitFieldTie', $obj; |
| 415 | .Ve |
| 416 | .PP |
| 417 | The contents of \f(CW$h\fR{'15:0'} would then be hex('0123'); |
| 418 | .Sh "\s-1EXPORT\s0" |
| 419 | .IX Subsection "EXPORT" |
| 420 | None. Object modules do not export any symbols. |
| 421 | .SH "SEE ALSO" |
| 422 | .IX Header "SEE ALSO" |
| 423 | \&\fIBit::Vector\fR\|(3). |